1. Field of the Invention
The invention relates to a method of cleaning contaminated soil, for example soil from a former gas works.
2. Description of the Prior Art
One example of contaminated soil is soil from land on which a gas works formerly stood. Such soils, for example, may contain about 4000 ppm complex bound cyanide, or about 3500 ppm polycyclic aromatic hydrocarbons. These contents far exceed the values prescribed in the Chemical Waste Act (CWA) of The Netherlands of 5 and 0.1 ppm respectively.
The method according to the invention is extremely suitable for cleaning these contaminated soils from a former gasworks, given as an example, but can also be used for cleaning other contaminated soil.
Various methods are known for cleaning contaminated soil.
In the so-called "glowing method", the soil is heated to a temperature in the range 200.degree. to 400.degree. C. The contaminations then escape in gaseous form, and are destroyed in a post-combustion chamber. The degree of cleaning which can be obtained by this method is unsatisfactory because of the very low temperature.
The "flushing method" and "flotation method" are other known methods, but when using these methods not only cleaned soil but also residual matter containing the contaminants are obtained. This residual matter is a chemical waste, according to the provisions of the CWA, which must be disposed of either by storage or by further processing.